This invention relates to a detection mechanism in a drive mechanism of a printer, for example, and in particular to a device for monitoring the reciprocating operation of a carriage on which a print head is placed.
Generally, a serial printer is provided with a motor (for example, a stepping motor, or the like) for reciprocally driving a carriage on which a print head is placed for printing on recording paper and includes a mechanism adapted to drive the carriage by the driving force of the motor via a transfer mechanism made up of gears, a belt, pulleys, or the like.
In such a mechanism, a controller in the printer transmits a drive signal for driving the motor. A detection mechanism monitors the normal reciprocating movement of the carriage in response to the motor driven by the drive signal.
Detection mechanisms 101 and 201, for example, as shown in FIGS. 13 and 14 have been previously known. As shown in FIG. 13, in the detection mechanism 101, a gear train 103 consisting of a plurality of gears for transferring the driving force of a motor is placed on a frame 102. A gear 104 is also placed on the frame 102 for rotation and is arranged to engage a specific gear of the gear train 103. A detection plate 105 shaped roughly like a disk is placed on a support shaft 104a of the gear 104 and rotates together with the gear 104. The edge of the detection plate 105 has a predetermined number of blades 105a and notches 105b. An optical sensor 106 of transmission type is placed at a position close to the detection plate 105 and a signal output in response to light cut off by the blades 105a of the detection plate 105 is compared with a drive signal of the motor, thereby monitoring the normal reciprocating operation of the print head.
As shown in FIG. 14, in the detection mechanism 201, a detection plate 205 shaped like the detection plate 105 is placed on a support shaft 203a of a specific gear 203b of a gear train 203 and an optical sensor 206 of transmission type detects a blade 205a of the detection plate 205 and similar processing is performed to determine whether or not the print head is normally reciprocating.
U.S. Pat. No. 5,090,829, Japanese Patent Publication No. 1-202462A, and Japanese Patent Publication No. 7-186478A also disclose detection mechanisms similar to those described above.
However, such related detection mechanisms involve the following problems:
For example, in the detection mechanism 101, the separate gear 104 is provided for the detection plate 105, increasing the number of parts. In addition, extra installation space for the gear 104 and the detection plate 105 becomes necessary, hindering miniaturization of the printer; which is a problem.
In the detection mechanisms 101 and 201, stray light from sunlight, a room light, or the like, can cause the optical sensor 106 and 206 to make detection errors. To prevent such detection errors, an additional member for protecting the optical sensor 106, 206 from stray light needs to be provided.
The optical sensor 106, 206 may be placed out of operation because of paper powder or lubricating oil used for maintaining the drive mechanism. Thus, close attention must be paid when lubricating oil is applied for maintenance.
The present invention is intended to solve such technical problems in the related mechanisms. It is an object of the invention to provide a high-reliability, small-sized detection mechanism capable of reliably blocking stray light and interfering substances, such as paper powder, or the like, without requiring an additional protection member for protecting a detector and a printer using the detection mechanism.
To accomplish the above object, according to the present invention, a detection mechanism is provided for monitoring a moving object comprising: a motor; a drive mechanism for transferring a driving force of the motor to move the object; a rotation body forming a part of the drive mechanism; a base for rotatably supporting the rotation body to define a substantially closed space there between; and a detector located in the closed space for monitoring the rotation of the rotation body.
With such a configuration, the rotation body reliably blocks the detector from the outside, forming an almost entirely enclosed inner space in cooperation with the base. When the rotation body is rotated, the detector detects the rotation of the rotation body within the space. Since the detector is blocked reliably from the outside in the entirely enclosed inner space of the rotation body, the high-reliability detection mechanism is capable of reliably blocking the detector from stray light and interfering substances such as paper powder, or the like, and of avoiding detection errors or detection failure of the detector without providing an additional protection member for protecting the detector. If lubricating oil is scattered with rotation of the rotation body, the detector placed within the rotation body is not affected at all, so that need to manage the amount of lubricating oil applied to the adjacent drive and transfer mechanisms can be avoided.
Further, the need to provide a member for protecting the detector and the desired part is eliminated, and there is no need to provide an additional detected part, so that the number of parts can be reduced, the installation space can be small, and the unit can be miniaturized.
Gears and pulleys of components of the drive and transfer mechanisms can be used as the rotation body of the invention. If a gear is formed with an inner space in which a detector can be enclosed by an integral molding of plastic, one part can provide the function of transferring a driving force, the function of a simple structure protecting the detector, and the function as a detected part. Thus, a compact detection mechanism can be provided and the problems in the related art of deposition and management of lubricating oil is advantageously avoided.
To form an enclosed space between the rotation body and the base supporting the rotation body, a concave region is formed in at least one of the sides of the rotation body and the base where they face each other. Preferably, the base side is formed with a concave part shaped like a circle which is concentric with the rotation body and has a diameter slightly larger than the diameter of the rotation body, and the rotation body is installed in the concave part, whereby the enclosure of the detected drive transfer member and the base can be enhanced and the detector can be more reliably protected.
The detection mechanism of the invention is particularly effective when an optical sensor is used as the detector, because the effect of stray light is eliminated.
To use an optical sensor of the transmission type, having a photo emitter and a photo receptor placed facing each other, the rotation body is provided with a detected part having a comb teeth-like shape and arranged so that the detected part passes through a clearance between the photo emitter and the photo receptor. In this case, if the detected part""s comb teeth shape is placed close to the rotation center of the gear, deflection of the projecting part of the teeth caused by rotation of the gear 11 is reduced; thus, the precision of detection of the projecting part is enhanced, making it possible to provide a detection mechanism of high precision.
On the other hand, using an optical sensor of the reflection type, having a photo emitter and a photo receptor placed adjacent to each other, the rotation body has a first segment and a second segment adjacent to each other and differing in their reflection of the light from the photo emitter. To make the reflection by the second segment different from that of the first segment, for example, the distance from the photo emitter or the light detection device to one segment can be made different from the distance from the photo emitter or the light detection device to the other segment. That is, the inner wall of the rotation body can be formed with a difference in level. When, for example, the gear and the detected are integrally molded part of plastic, or the like, and the inner wall of the gear is formed with a difference in level, the invention can be easily embodied so that high dimension precision is not required, mold manufacturing, etc., is facilitated, and a cost advantage is obtained.
The segments can be made different in reflectivity without forming such a difference in level. For example, a monochrome stripe can be printed radially on the inner wall of the gear. In this case, for example, the inner wall of the gear need not be formed with a difference in level, thus mold manufacturing, etc., is facilitated and, in addition, the precision of the optical sensor for detecting the detected part can be enhanced.
The detection mechanism of the invention can be used with a printer comprising: a print head for printing on recording paper; a carriage on which the print head is mounted; a motor; and a drive mechanism for transferring the driving force of the motor to reciprocally move the carriage. The above-described detection mechanism can be connected to the drive mechanism of the carriage and a controller can compare an output pulse of the detection mechanism with a drive pulse of the motor and monitor the operation of the carriage. Thus, a high-reliability, small-sized printer protected from the effect of stray light and interfering substances such as paper powder, or the like, is provided in a simple configuration.
In a printer further including a ribbon transport mechanism for transporting an ink ribbon and a transfer mechanism being connected to the drive mechanism for reciprocally moving the carriage to transfer the driving force of the motor to the ribbon transport mechanism, with the rotation body of the detection mechanism placed in a part of the transfer mechanism, trouble occurring in transporting the ink ribbon can be detected.